A synchronous rectification type DC-DC converter that includes a metal oxide semiconductor field effect transistor (MOSFET) in place of a rectifying diode is known. FIG. 13 is a schematic diagram showing the configuration of a synchronous rectification type DC-DC converter. The illustrated DC-DC converter 100 includes a high-side MOSFET 110, a low-side MOSFET 120, a Schottky barrier diode (SBD) 130, a coil 140, a capacitor 150, and a control IC 160. The DC-DC converter 100 is controlled by the control IC 160 so as to alternately supply current to the high-side MOSFET 110 and the low-side MOSFET 120, to reduce the voltage.
The conventional DC-DC converter 100 is made by mounting the foregoing functional devices on a printed circuit board, and then electrically connecting the electrodes of each functional device via wiring formed on the printed circuit board.
The internal structure of the high-side MOSFET 110 may be made like a MOSFET described in patent document 1 below. In that case, the high-side MOSFET 110 is configured as shown in FIG. 14. Specifically, the high-side MOSFET 110 includes a MOSFET chip 111, a frame 112, a gate terminal 110a, a source terminal 110b, and a drain terminal 110c. The gate electrode and the source electrode of the MOSFET chip 111 are connected directly to the gate terminal 110a and the source terminal 110b, respectively. The drain electrode is connected to the drain terminal 110c through the frame 112. The low-side MOSFET 120 may be configured in a similar manner.
Patent Document 1: JP-A-2002-76195
As stated above, in the conventional DC-DC converter 100, the functional devices are electrically connected through the wiring formed on the printed circuit board. Generally, the wiring formed on the printed circuit board has certain wiring resistance and inductance. The wiring resistance is proportional to the length of the wiring, and inversely proportional to the cross-sectional area thereof. The wiring inductance is substantially proportional to the length of the wiring. Even if the high-side MOSFET 110 and the low-side MOSFET 120 are mounted adjacently on the printed circuit board, there is a limit to the reducible amount of the resistance and the inductance of the wiring between the source terminal 110b of the high-side MOSFET 110 and the drain terminal 120c of the low-side MOSFET 120.
The wiring resistance leads to an increase in power consumption of the DC-DC converter 100, and the wiring inductance leads to deterioration of switching performance of the DC-DC converter 100. In addition, the wiring inductance may cause electromagnetic interference (EMI). Specifically, the wiring inductance generates a magnetic field, and when the magnetic field fluctuates, noise is generated in the circuit. Such noise degrades the performance of the DC-DC converter 100.
Further, the frames 112, 122 provided inside the respective MOSFETs 110, 120 also have the wiring resistance and the wiring inductance. This makes the foregoing issue more serious. In particular, when the DC-DC converter 100 is used for high-frequency applications, the influence of the wiring inductance becomes greater.